Positive Political Theory I is concerned with the formal theory of preference aggregation for collective choice. The theory is developed as generally as possible, covering classes of aggregation methods that include such well-known examples as majority and unanimity rule and focusing in particular on the extent to which any aggregation method is assured to yield a set of best alternatives. The book is intended both as a contribution to the theory of collective choice and a pedagogic tool. Austen-Smith and Banks have made the exposition both rigorous and accessible to people with some technical background (e.g., a course in multivariate calculus). The intended readership ranges from more technically-oriented graduate students and specialists to those students in economics and political science interested less in the technical aspects of the results than in the depth, scope, and importance of the theoretical advances in positive political theory.